This is a very simplified overview of the factors that initiate cancer.

Cancer is the uncontrolled growth of cells. As any other cellular
function, growth is controlled by genes. Genes are codes within DNA. DNA
is a large string like molecule comprised of four basic molecules
(Adenine, Timin, Guanine, Cytosine). They are combined in a chain like
formation so that a part of a large DNA molecule may look like
..ATTACG..., where letters stand for the four basic molecules of the
DNA. Entire DNA is divided into 46 smaller sub strings called
chromosomes. Sub-substring of chromosomes are called genes. They control
all cellular functions.

Every normal cell in our body has all genes, because all cells became
from the one cell - fertilized egg (called zygote). However,
not all genes are active in all cells. Certain genes are deactivated in
certain cells, if they control functions not required by the specific
cell.

Also, some genes are only active during certain periods of cellular life.
These genes control cellular growth and multiplication. If they are
hyperactive, cell will divide uncontrolled. Some genes have the ability
to suppress the activity of other genes. If these genes are deactivated,
cell will also divide uncontrolled.

Genes can be deactivated if the DNA molecule is damaged at the very
location of the gene. This can be caused by the radiation or some
substances called carcinogens. Damaged DNA will be repaired in normal
cells, unless the damage is too big, but if this mechanism is damaged
too, the repair will not be successful. Certain genes can be introduced
into human cells, usually by viruses. This genes can then cause cellular
growth. This is thought to be the mechanism of cervical cancer
formation, where the Human Papiloma Virus (HPV) act as a carrier of some
genes (oncogenes) and inserts them into human cells.

It is considered today that high levels of female sex hormone estrogen
may lead to an increase in mass and number of the uterine lining cells
if there is not enough progesterone, another important sex hormone in
women.

In normal menstrual cycles, which are 28 days long in average, there are
two phases: in the first 2 weeks estrogen is predominant sex hormone and
it causes the cells of the lining to grow and increase in number. Next
14 days or so, the predominant sex hormone is progesterone. It causes
cells to mature, so that the uterine lining can accept and nourish the
fertilized egg.

However, if there is not enough progesterone, cells of the uterine
lining (the epithelium) will simply grow and multiply more and more.
That is called hyperplasia simplex - a simple growth. If that
situation goes on, new glands in the lining will be formed. That is
called hyperplasia complex - a complex form of growth. Finally, if
cells become atypical, showing some strange behavior, then
we talk about atypical growth. So there are:

High estrogen levels without enough progesterone can be found in some
diseases or conditions like: long term anovulation, obesity, excessive
long term estrogen intake or tumors producing estrogen, thyroid
malfunctions and liver diseases.

EC may grow on the surface of the lining, filling the uterine void, or
may invade the muscular layer of the uterus, which depends on how well
differentiated EC is. Less differentiated ECs have less characteristics
of the normal lining cells and therefore do not behave like ones.

EC also spreads through the lymphatic and venous blood vessels. Former
are thin vessels filled with lymph (see-through liquid), and the latter
contain venous blood. Cells of the carcinoma get detached from the main
mass and are taken by the flow to other organs and parts of the body.
Such metastases may invade ovaries, or vagina (especially in the lower
third). The latter may be the first sign of EC and thereby indicate
further action.

EC can spread to other organs like liver, lungs, brain or bones. Such
metastases can be removed surgically if they are single. However,
occurrences of such metastases worsen the prognosis.

Grade is a degree of differentiation. Normal cells have genetic
instructions to multiply with certain speed and to interact with other
cells in a certain way. Cancer cells do not behave like normal ones and
therefore they are less differentiated. Well differentiated cells that
look and behave almost like normal cells are called well differentiated.

If a tumor consists of glandular formations, with less than 5% solid
parts it is called Grade I. Grade III consists of more than 50% solid
parts, and Grade II lies in between. Normal endometrial lining consists
of glandular formations that secrete mucous like substance that
nourishes fertilized egg before implantation.

Stage determines how far has EC extended locally. Adjacent organs like
urinary bladder or intestines may also be affected later on. At the
beginning of illness, EC consists of cells located in the lining. As
tumor grows, it affects the muscular layer of the uterus and then the
cervix, vagina and other organs and tissues.

Stage 1:

1a - tumor is restricted to endometrium (uterine lining).
1b - it affects less than one half of the muscular layer thickness.
1c - it affects more than one half of the muscular layer thickness.